1. Technical Field of the Invention
This invention relates generally to systems and methods for testing devices utilizing radio frequency signals.
2. Description of the Related Art
Performing testing on devices utilizing radio frequency signals, for example radar sensors or antenna systems, may involve outdoor testing, in controlled conditions and/or in large buildings, under conditions simulating actual use of the antenna. However, testing outdoors or in a large building under controlled conditions is often impractical and/or expensive, and thus smaller indoor test ranges are often desired and used for testing.
The simplest type of prior art indoor testing facility involves surrounding an interior space with radar-absorbing material, and relying on direct illumination of a sensor by an antenna or antenna array in performing testing. The sensor may be rotated and/or moved in order to examine the effect of orientation and movement on antenna performance. Such a direct illumination test facility has the disadvantage of requiring a large interior space, as well as a significant quantity of radar-absorbing material.
Another type of prior art indoor test range for testing sensors (a compact range) uses one or more curved metal mirrors (or curved shapes coated with metal) illuminated by one or more antennas to collimate the energy and achieve the same effect on a test zone as would be achieved by a far field source (as in an outdoor range). The use of mirrors reduces the size of the test range, relative to ranges without metal mirrors. However, such indoor test ranges have a limited field of regard (nominally about seven to ten degrees) which limits the field of regard for the sensor. This limitation on the field of regard for the sensor is a severe limitation for performing hardware in the loop testing (also known as HWIL, HIL, or HITL testing) against targets generated by an array of antennas. Also, an expensive high quality reflective mirror may be required to achieve a high level of performance. A high quality reflector dish requires an edge treatment (to reduce energy bouncing off the edge of the mirror and mixing—out of phase—with the direct reflection from the surface). The edge treatment of the mirror has to handle not only the diffraction effects of direct illumination, but the diffraction effects of energy traveling along the surface of the mirror to the edge. In order to achieve larger angular coverage with a reflective mirror, extremely expensive custom designs must be resorted to, and even then there are performance limitations.
From the foregoing it will be seen that improvements are possible in the field of radio frequency test facilities, especially when applied to HWIL.